The present invention generally relates to deployable space structures and booms and more specifically provides structural support to tubular open-section boom systems.
Spacecraft systems, which include earth and planetary orbiting satellites and deep space probes, often incorporate deployable systems which include deployable structures, deployable solar arrays, deployable antennas, and other deployable subsystems. These deployable systems must be configurable between a storage configuration that enables the entire spacecraft system, inclusive of the deployable structure, to fit within the small volume constraints of a launch vehicle, and a deployed operable configuration that enables the spacecraft to function in a desired manner once in space.
Once the spacecraft is in space, the spacecraft is typically configured for use by deploying an assembly of extendable deployable components. For example, the assembly of extendable components may comprise an extended solar panel or blanket array that is used to convert collected solar radiation into electrical energy. In another example, the assembly of extendable components may comprise an extendable antenna assembly that is used to transmit and receive electromagnetic signals to and from a plurality of earth-based installations. In yet another example, the assembly of extendable components may comprise an extendable boom assembly that is used as a platform for a critical sensor, such as a magnetometer or electric field sensor.
The deployable boom assemblies are required to compactly stow into a small volume and then reliably deploy in a known kinematic manner to form a rigid and strong appendage of the spacecraft. The boom assemblies must also be lightweight so they can be launched into space, and low cost so they can be affordable to the program. Further complicating the design of these devices, emerging space missions require deployable systems of increased size and load-carrying capability while minimizing program costs.
One type of deployable boom assembly comprises a metallic tubular slit boom. Metallic tubular slit booms have been used in the space industry to deploy sensors and in some cases as structural elements within a larger deployable system. Due to the open-section nature of the tubular slit boom accompanied by the characteristic base mounting of the tube to the spacecraft, a linear or near-linear pattern of fasteners opposite the tube slit have been typically used for applications with lower loads and orbital accelerations. Recently, slit booms of composite reinforced construction have been developed that offer increases in deployment force, torque and thermal stability. However, the thin-wall nature of the metallic or composite reinforced slit tube and localized bending of the tube forward of the conventional base mount limits the bending load-carrying capability of the slit tube. In addition, the standard boom mounting allows the free edges of the slit boom to translate relative to each other when a torsional load is applied to the boom tip significantly reducing the torsional stiffness of the boom.
Various approaches have been utilized to address these issues. At the system level, slit booms may be used effectively in pairs so that they are loaded primarily in bending due to the low torsional stiffness of each individual boom. For higher load applications, open lattice, articulated or potentially telescoping booms are used. These boom types are comprised of multiple and complex deploying elements that are arranged in a repetitive manner to form a boom of desired length. However, the open lattice, articulated and telescoping boom technologies are high cost and labor intensive to manufacture. They consist of a large number of moving parts that may inherently reduce the deployment reliability of the boom system. As increasingly advanced types of spacecraft are being developed, it has become apparent that currently boom technologies are insufficient for meeting emerging applications in terms of cost, reliability, stiffness and strength.